This invention relates, generally, to the field of semiconductor devices and more particularly to metal-insulator-metal (MIM) capacitors as used in semiconduct or devices.
As semiconductor devices shrink, there is a desire to decrease the area occupied by features, such as capacitors. To accommodate, capacitors are being formed over transistors (e.g. at the metal level) as opposed to being formed at the transistor level nearer the bulk semiconductor substrate. One example of such a capacitor is a metal-insulator-metal (MIM) capacitor. At the metal level, polysilicon cannot be used as an electrode material because deposition of polysilicon is a high temperature process that is not compatible with back-end (post-metal) processing. Copper is replacing aluminum and aluminum alloys as the predominant material for metal interconnects in semiconductor manufacturing. Therefore, it would be advantageous to use copper as the metal of a MIM capacitor electrode to avoid having to add further materials and processing steps. However, there are problems associated with using copper in conjunction with many of the high dielectric constant materials which are desirable for use in a MIM capacitor, particularly capacitors used in RF applications that require high capacitance linearity. A highly linear capacitance is one that is constant as a function of applied voltage and frequency. Known problems with using copper as an electrode material include adverse affects caused by poor mechanical and chemical stability of the copper surface, and other interactions of the copper with the capacitor dielectric materials (e.g. copper diffusion).
Therefore, a need exists for a MIM capacitor structure which includes use of copper as a capacitor electrode in which the fabrication can be easily integrated with the rest of the semiconductor manufacturing sequence, which results in a capacitor with high linearity and high capacitance, and which alleviates many of the problems associated with having copper as one of the capacitor electrodes.